Power theft (non-technical losses (NTL)) is a significant problem for power distribution systems. The amount of theft can be as much as half of all energy supplied in some localities. The most common type of power theft occurs when consumers draw power directly from power lines between a distribution transformer (DT) and a power meter, so the illegally consumed power cannot be measured, and billed.
In general, the mismatch between the total energy supplied by the DT and the sum of energy consumed by all metered consumers can be detected, and the total amount of losses, technical and non-technical, in the distribution system can be estimated.
However, this amount includes both technical losses that are inevitable during the normal operation of the power distribution system, and the NTL. Technical losses comprise the Ohmic losses in the power lines due to the resistance of the lines, conversion losses in intermediate devices, leaks due to imperfect isolation, etc. Because some of the components of the technical losses depend on the amount of energy delivered to the consumers, and that amount varies significantly over time, it is generally difficult to determine what part of the total power loss is technical, and what part might be due to NTL.
It would be possible to determine accurately the exact amount of technical losses if all the parameters of the power distribution system are known, including its connection topology, order and attachment points of all consumers, the line resistances between the attachment points, as well as the instantaneous power consumption by every consumer at any moment in time.
In practice, full knowledge of these parameters is economically and technically infeasible. A power utility normally knows which consumer is served by which DT from the connecting topology, but the connection order and exact line resistances would not normally be known. In addition, full knowledge of the power consumption by any consumer at any instant in time would only be possible by installing detailed measurement equipment that performs very frequent measurements (multiple times per second). Such an installation would be prohibitively expensive with costs far exceeding the cost of power theft.
In practice, utilities measure power consumption only infrequently, e.g., every month for conventional meters and every 30 minutes for smart meters. The most important measurement available to power utilities is the total amount of active power consumed by a consumer during the measurement interval, because this value is the basis on which payment by the customer is determined.
Additional variables provided by some meters, for example smart meters conforming to the ANSI C12.19 standard, comprise reactive power consumed by the consumer (important for billing of some industrial customers), instantaneous voltage and current at the beginning and end of the measurement interval, power quality information, and the like.
A number of prior art methods for power theft detection are known, based on the limited set of measurements. One method estimates total power losses by balancing energy supplied by the DT, and the power consumed by all metered consumers, and determine the loss rate as a percentage of the total amount of energy provided. When this loss rate exceeds a specified threshold, e.g. 3%, then theft can be suspected and investigated.
A disadvantage of that method is that no distinction is made between technical and non-technical losses, so when technical losses are unusually high for good reasons, for example very uneven power consumption, the power theft could be detected erroneously.